1. Field of the Invention
The present invention generally relates to medical devices, and more specifically relates to implantable prostheses and tissue expanders.
2. Description of the Related Art
Implantable prostheses are commonly used to replace or augment body tissue. In the case of the female breast, it may become necessary to remove some or all of the mammary gland and surrounding tissue in order to treat breast cancer. This surgery leaves a void that can be filled with an implantable prosthesis that supports surrounding tissue and provides a normal body appearance, eliminating much of the shock and depression that often follows breast cancer surgeries. Implantable prostheses are also used for breast augmentation procedures.
Tissue expanders are implantable devices that are placed beneath the skin and then gradually inflated to stretch the overlying tissue. Tissue expanders are commonly used to either create a pocket for receiving a permanent prosthesis or to generate an increased skin surface area in anticipation of the new skin being utilized for grafting or reconstruction. After implantation, a solution, such as saline, is periodically injected into the tissue expander to increase the volume of the expander. Between injections, the surrounding skin is permitted to stretch and grow to create the increased skin surface. The solution may also be withdrawn from the tissue expander to reduce its volume.
Implantable prostheses and tissue expanders are usually formed of a silicone shell. Such devices are typically manufactured by dipping an appropriately sized and shaped mandrel into a biocompatible elastomer, such as silicone. Once the shell has been formed, it is removed from the mandrel. The dip-molding process results in the formation of a shell that has a mandrel opening, e.g., a circular hole, in one of its faces. The mandrel opening is subsequently covered with a patch that seals the hole to form a fluid impervious implant shell. The patch may be attached to the implant shell using silicone rubber or other similar biocompatible adhesives. The completed shell can remain unfilled, be pre-filled, or intraoperatively filled through a small fill port or valve with a solution such as saline, gel, foam, or combinations of these materials.
Valve assemblies are often used for post-operative filling and adjustment of implantable prostheses and tissue expanders. The valve assemblies used in these implants tend to be large and palpable. Permanent implants, e.g., breast implants, have filling tubes which may be used to add and withdraw fluid, however, these implants typically do not allow for adjustment after the filling tube is removed. As such, the pathway left after withdrawal of the tube is permanently closed.
There have been many efforts directed to providing valves for implants. U.S. Pat. No. 4,263,682 discloses a self-sealing valve for a fluid fillable implant, such as a mammary prosthesis, having first and second planar members that are bonded together in such a manner that leaves a bonded region and an elongated, unbonded region therebetween. Openings are formed in the planar members of the valve to provide for communication between the unbonded region and the inside and outside of the valve. The openings are offset from one another so that the openings and the unbonded region form a normally open channel through the valve. At least one of the planar members is sufficiently flexible to close the normally open channel is response to fluid pressure from within a fluid filled implant. Unfortunately, in use, it has been observed that the interior fluid pressure is not sufficient to prevent leakage of fluid through the valve.
In spite of the above advances, there remains a need for prosthetic implants and tissue expanders having valves that facilitate adding and removing solution from the implant shell. In addition, there remains a need for implants and tissue expanders having valves with a low profile, that are minimally palpable, and that are highly leak resistant. There also remains a need for prosthetic implants and tissue expanders having valve assemblies that enable solution to be easily added and removed both before and after implantation.